---
title: "Refund a transaction from the POS"
url: "https://docs.adyen.com/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/cancel-or-refund-a-transaction-c-library/refund-a-transaction-from-the-pos-c"
source_url: "https://docs.adyen.com/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/cancel-or-refund-a-transaction-c-library/refund-a-transaction-from-the-pos-c.md"
canonical: "https://docs.adyen.com/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/cancel-or-refund-a-transaction-c-library/refund-a-transaction-from-the-pos-c"
last_modified: "2026-05-24T12:54:31+02:00"
language: "en"
---

# Refund a transaction from the POS

[View source](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/key-steps-c-library/cancel-or-refund-a-transaction-c-library/refund-a-transaction-from-the-pos-c.md)

## Implement the callback

Implement the callback based on the signature in the **cancel\_or\_refund\_extern.h** file and pass this as a parameter of the **cancel\_or\_refund** call. For more information on how to do this, see [Implement callbacks](/point-of-sale/classic-library-deprecation/classic-library-integrations/c-library-integration/calls-and-callbacks-c-library/implement-callbacks).

## Allocate the request struct

Allocates, initializes and returns a `cancel_or_refund_request` struct. Populate the request by performing string duplication.

If you want the data for later use, retain it, or it will be released automatically.

| Name                        | Description                                                                                                                                                                                                        |
| --------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `cancel_or_refund_allocate` | Allocates, initializes and returns a `cancel_or_refund_request` struct. Populate the request by performing string duplication.If you want the data for later use, retain it, or it will be released automatically. |

## Call the cancel\_or\_refund Function

Call the `cancel_or_refund` function to initiate a cancel or refund on a transaction that has been processed by the Adyen payments platform.

### Parameters

| Value                       | Description                                                                                                                                                                                     |
| --------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `cancel_or_refund_request`  | Pointer to the `cancel_or_refund_request` struct, this struct contains all the input parameters for this call.                                                                                  |
| `cancel_or_refund_response` | Pointer to the callback function in the POS that will be called with the results of the `cancel_or_refund` call                                                                                 |
| `echo_struct`               | Pointer to a POS defined struct. Returned in the callback. It can be used to share a POS data struct between the call to the library and the callback from the library in response to the call. |

## Handle the callback

The `cancel_or_refund_CB` returns the immediate response to the call and a pointer to the POS-defined echo struct.

### Parameters

| Value                       | Description                                                                                                                                                                                                         |
| --------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `cancel_or_refund_response` | Pointer to the callback function in the POS that will be called with the results of the `cancel_or_refund` call. If the refund was successful, this struct should should return a result of "**refund-received**".  |
| `echo_struct`               | Pointer to a POS defined struct. Returned in the callback. It can be used to share a POS data struct between the call to the library and the callback from the library in response to the call.                     |